A field trial of commercially available fluorogenic substrate reagent kits and dedicated fluorometer was undertaken to evaluate this system's appropriateness to our research and clinical care efforts. Synthetic substrate for proteolytic enzymes can be made. The substrates are then tagged with a chromogenic or fluorogenic group such that after cleavage of the substrate the active group is released and becomes chromatically active or fluorescent. The rate of release of the group is proportional to enzyme concentration in a substrate excess assay. Many coagulation or fibrinolytic enzymes are proteolytic. Of particular interest are thrombin and plasmin. Assays for heparin and antithrombin III can be generated by adjusting reagents such that they are the rate-limiting factors in generation of thrombin. The current results of our evaluation showed a drift and variability in the baseline zero for heparin and antithrombin III which was determined to be unacceptable. The accuracy and precision was also not clinically acceptable. Adjustments in the substrate-reagents mixture or the instrument electronics may be necessary to correct these deficiencies. The plasminogen, plasmin assays were only briefly evaluated but appear promising as rapid, stable, reliable assays.